Many mammals, including humans, have suffered the action of mosquitoes. The blood sucking of mosquitoes results in an itching sensation and often a rash. Also, many mosquitoes cause potentially life-threatening illness. Aedes aegypti can cause dengue fever and yellow fever, Anopheles quadrimaculatus can cause malaria and Culex quinquefasciatus can cause West Nile disease. One possible solution to these problems is applying a mosquito repelling agent to the skin as a topical repellent. Applying repellents to fabric, like mosquito netting, is another way of reducing mosquito bites.
DEET®, namely N,N-Diethyl-m-toluamide, is widely used against mosquitoes, but is characterized by an unseemly bad smell, is not particularly long lasting in its effect and it dissolves plastics. Moreover, several safety questions have been raised concerning the use of DEET® and some governments have restricted the amount of the active component that may be employed in formulations. This itself presents a further problem since DEET® is subject to evaporation and it needs to be formulated at higher than effective dosages in order to maintain its effectiveness. Furthermore, many insects and pests have developed resistance to DEET® due to its wide spread usage.
As such, there is a need to provide a mosquito repellent formulation which is non-toxic to the people, plants, and other animals which may be exposed to areas of application. A further need is for a mosquito control formulation that comprises long lasting effects, thereby limiting the need for frequent re-application to treated areas.
Consumer research regarding the key attributes of topically applied insect repellents strongly suggests that consumers prefer products with high efficacy, long-lasting protection, safety in use, and odorless when applied to skin. Leading insect repellent products currently available to consumers claim to meet these requirements but almost always disappoint the user for having unacceptably strong odor on skin.
It must be noted that over the years Researchers have identified ingredients which either matched or exceeded repellency of DEET®, such as for example, U.S. Pat. No. 6,660,288. These were basically fragrance ingredients with added functionality. In the end, these materials failed to become acceptable repellents mainly because of their high cost or intolerably strong odor at levels required to achieve an acceptable level of repellency.
One ingredient among this class of repellents is methyl dihydrojasmonate. It is a well-recognized fragrance ingredient described as having a strong jasmine odor with a citrus freshness. Its popularity as a fragrance ingredient has helped it to become a leading fragrance ingredient representing use volumes in thousands of tons a year. While an elegant fragrance material, its odor intensity represents a problem in using it as a repellent at the required levels of ˜15% to match DEET efficacy. It was therefore very surprising to find that propyl dihydrojasmonate, a homolog of methyl dihydrojasmonate, was virtually odorless.